(i) FIELD OF THE INVENTION
This invention relates to a telescope operating system capable of assisting an observer to locate stars or other celestial bodies. The invention specifically concerns an apparatus and method for operating an optical telescope, and an optical assembly for use with such an operating system.
(ii) DESCRIPTION OF THE PRIOR ART
As is known, most astronomical telescopes comprise two main parts: the optics and the mounting. The optics on modern telescopes generally consist of extremely accurate mirrors. Light reflected from the mirrors is brought to a focus outside the instrument, where an eyepiece, camera, or other instrument may be mounted. Focusing is done by varying the distance between the primary mirror and the eyepiece.
The mounting of the telescope may be in one of several configurations. Most telescope designs utilize some variation of the Equatorial mounting. Such mountings have a Polar or Right Ascension axis carefully aligned to be parallel with the poles of the earth, and a perpendicular Declination axis. The terms Right Ascension and Declination refer to the equivalents of Longitude and Latitude in the celestial coordinate system. The position of the telescope can be determined directly by measuring the angular position of the telescope axes. Declination is usually measured in hours, minutes, and seconds of the Vernal Equinox. The Vernal Equinox is the prime meridian for the celestial coordinate system, corresponding to the direction of the sun at the spring equinox. The position of the telescope will usually be adjustable by means of motors, one for each axis.
One conventional method of locating a celestial body was to use a paper star chart or catalog, and manually to adjust the telescope using either setting circles or using a wider-field finder telescope. An improvement on this method was the Planisphere which operated as a small, flat planetarium, allowing the user to rotate the chart through a window to see the sky as it appeared at a particular latitude at any date and time. Another improvement was the use of a computer program to plot the star maps. In large observatories, sophisticated control systems, with micro-controllers used in conjunction with star and celestial body data bases allowed the user to enter coordinates or a designation of the celestial body, and the telescope would automatically slew to the desired location. These systems tend to be expensive and so not generally applicable to smaller telescopes.
The patent literature has also disclosed some improvements in star tracking.
U.S. Pat. No. 3,578,975 patented May 18, 1971 by The Perkin-Elmer Corporation provided a telescope guiding and focusing apparatus in which guiding and focusing errors in a stellar telescope were detected automatically using photo-electric techniques. Light from a guide star, collected by a telescope, was directed out of the telescope as a converging focusable beam and impinged on a high-speed chopping element. Guiding errors were detected by measuring the intensity of the emerging chopped light. An AC component in the output signal indicated a guiding error. Focusing errors were detected by measuring the intensity of the emerging chopped light after it struck and was partly blocked by a knife edge positioned where the focus should occur. An AC component in the output signal indicated a focusing error. Both output signals were either read on meters, or were fed into servosystems which moved portions of the telescope to compensate for the errors.
U.S. Pat. No. 3,609,374 patented Sep. 28, 1971 by Singer-General Precision provided a star tracking system including detectors arranged in a linear array perpendicular to the scanning path to sample the field of view, either mechanically or electrically until a presumed star signal was detected. At that time, the array or its image retrogressed a short distance and re-scanned only a very small segment of the field of view several times. If the signal actually was a star signal, it would be detected at the conclusion of the re-scanning. If it were not, the search would continue until the star was acquired. Using such scanning technique, the signal-to-noise threshold was set comparatively low, for example, at one-half the signal-to-noise ratio ordinarily used, thereby greatly increasing the background brightness capability. The system was arranged both to raise the threshold to a relatively high signal-to-noise ratio and to change the matched-filter-bandwidth, when the scanner retraced to make its subsequent passes. This was thus a device used for tracking the position of a star using a small telescope.
U.S. Pat. No. 3,626,192 patented Dec. 7, 1971 by The Bendix Corporation provided a star tracker having an aperture for receiving and diffracting starlight and daylight. Interference fringes were formed from the starlight because of its coherent nature. A phase shifter was positioned to intercept a portion of the diffracted light and to phase shift the intercepted light in response to a signal causing the interference fringes to be modulated in accordance with the signal. Photodetectors sensed the fringe modulation and provide modulated outputs which were then demodulated to provide DC voltages corresponding to the intensity of the detected interference fringes. The DC voltages were subtracted and the remainder was used to energize a servo motor to aim the star tracker at a star.
U.S. Pat. No. 4,187,422 patented Feb. 8, 1980 by the Singer Company provided a self-calibrating star tracker in which a light signal source located on the detector was reflected into the optics and was redirected from the optics back onto the detector. In this manner, movement of the detector or optics from a known position could be sensed and calibration of the instrument could be conducted at any time. Such star tracker was proposed to be used with an inertial guidance system which included both a detector and optics.